In 1953, it was first recognized that ingestion of gluten, a common dietary protein present in wheat, barley and rye causes a disease, now called Celiac sprue, in sensitive individuals. Gluten is a complex mixture of glutamine- and proline-rich glutenin and prolamine molecules, which is thought to be responsible for disease induction. Ingestion of such proteins by sensitive individuals produces flattening of the normally luxurious, rug-like, epithelial lining of the small intestine known to be responsible for efficient and extensive terminal digestion of peptides and other nutrients. Clinical symptoms of Celiac sprue include fatigue, chronic diarrhea, malabsorption of nutrients, weight loss, abdominal distension, anemia, as well as a substantially enhanced risk for the development of osteoporosis and intestinal malignancies (lymphoma and carcinoma). The disease has an incidence of approximately 1 in 200 in European populations.
A related disease is dermatitis herpetiformis, which is a chronic skin eruption characterized by clusters of intensely pruritic vesicles, papules, and urticaria-like lesions. IgA deposits occur in almost all normal-appearing and perilesional skin of individuals with this disease. Asymptomatic gluten-sensitive enteropathy is found in 75 to 90% of patients and in some of their relatives. Onset is usually gradual. Itching and burning are severe, and scratching often obscures the primary lesions with eczematization of nearby skin, leading to an erroneous diagnosis of eczema. Strict adherence to a gluten-free diet for prolonged periods may control the disease in some patients, obviating or reducing the requirement for drug therapy. Dapsone, sulfapyridine and colchicines are sometimes prescribed for relief of itching.
Celiac sprue is generally considered to be an autoimmune disease, and the antibodies found in the serum of the patients support a theory of an immunological basis for the disease. Antibodies to tissue transglutaminase (tTG) and gliadin appear in almost 100% of the patients with active Celiac sprue, and the presence of such antibodies, particularly of the IgA class, has been used in diagnosis of the disease.
Gluten is so widely used, for example in commercial soups, sauces, ice creams, hot dogs, and other foods, that patients need detailed lists of foodstuffs to avoid and expert advice from a dietitian familiar with celiac disease. Ingesting even small amounts of gluten may prevent remission or induce relapse. Supplementary vitamins, minerals, and hematinics may also be required, depending on deficiency. A few patients respond poorly or not at all to gluten withdrawal, either because the diagnosis is incorrect or because the disease is refractory. In the latter case, oral corticosteroids (e.g., prednisone 10 to 20 mg bid) may induce response.
One candidate for protease therapy is EP-B2 (Endoprotease B, Isoform 2), a papain-like cysteine protease that facilitates gluten breakdown and assimilation in germinating seeds of Hordeum vulgare (barley). In vitro and in vivo studies have shown that the zymogen (pro-EP-B2) form of this enzyme rapidly self-activates under gastric conditions, where mature EP-B2 can effectively detoxify gluten at pharmacologically reasonable doses (<5% w/w) (Bethune et al. (2006) Chem. Biol. 13(6):637-47; Gass et al. (2006) J Pharmacol Exp Ther. 318(3):1178-86). Controlled clinical studies to demonstrate the utility of this enzyme as supportive therapy for Celiac Sprue patients require relatively large amounts of enzyme, however, and there remains a need for methods to produce the enzyme in such amounts. The present invention meets this need.